1. Field of the Invention
The invention is concerned with force-fit joints formed between tubing and metallic members such as flanges and more particularly it is concerned with joints of increased torque resistance between tubing and flanges and with a unique and novel process for producing such an improved torque resistant joint by utilizing powdered metal for the formation of the flange portion thereof.
2. Prior Art
The prior art teaches any number of tubing-flange joints. A number of such joints are obtainable wherein the joint has a circular cross section hole therethrough adapted to receive an end of the tube, the hole having at least one annular channel extending therefrom into the flange, by placing an end of the tube within the hole, the end having an external diameter very nearly equal to the diameter of the hole and the tube being formulated of a less hard metal than the flange and forcing an expanding means into the end of the tube and thereby forming a force-fit joint between the exterior of the tube and the hole through the flange. Generally, the prior art flanges have been formulated by machining from metal of a desired hardness, for example, of hardness Rockwell B90 (hardness as referred herein is as measured by ASTM E 18). Such joints have occasionally developed leaks due to lack of a sufficient resistance of the joint to torque which is encountered in many everyday operations using said joint. For example, when said joints are part of the hydraulic systems of heavy earth moving equipment, they are often subjected to sharp torque strains which cause the joints to break loose thus leading to leaking about the joints. Also it is quite expensive to make the flanges for such joints because of the high cost of machinists' labor, especially on machined flanges made of relatively hard metal.
Powdered metal has been used to form a number of parts but has generally not been used for the flanges because of the generally porous nature thereof which is evidenced by a density lower by about 10% than the density of machined metal flanges and because while the outer layer of formed powdered metal parts are known to be hardened, said outer layer is generally very thin and thus one would be led to expect to obtain a weaker joint when using powdered metal than when using machined metal.
Surprisingly, it has been found that when the flange portion of the joint is made from formed powdered metal, the resulting joint is significantly more torque resistant than are similar joints made using identically shaped flanges which are formed from machined metal of substantially the same or even considerably higher measurable Rockwell B hardness as the powdered metal flanges. Since powdered metal flanges are also less expensive than machined metal flanges, this provides a significant and important practical as well as structural advantage.